How to check a child exist in firebase database using Android

Firebase makes this nice and easy. Depending on how your database is structured, you could do something like this. An example for a social media style application, where we need to check multiple times if a value exists. If you only need to do it once, you can use a SingleValueEvent listener.

First, instantiate a ValueEventListener and inside the onDataChange method check if the value exists.

1. ValueEventListener responseListener = new ValueEventListener() { 
2. @Override  
3. public void onDataChange(DataSnapshot dataSnapshot) { 
4. if (dataSnapshot.exists()) { 
5. // Do stuff  
6. } else { 
7. // Do stuff  
8. } 
9. } 
10.  
11. @Override  
12. public void onCancelled(DatabaseError databaseError) { 
13.  
14. } 
15. }; 
16.  
17. FirebaseUtil.getResponsesRef().child(postKey).addValueEventListener(responseListener); 

Then add the listener to the correct reference in the database. Above, I am adding it to:

1. public static DatabaseReference getBaseRef() { 
2. return FirebaseDatabase.getInstance().getReference(); 
3. } 
4.  
5. public static DatabaseReference getResponsesRef() { 
6. return getBaseRef().child("responses"); 
7. }